The present invention relates to a sealed type liquid cooling apparatus which can individually cool each chip in a semiconductor multichip module in which a plurality of semiconductor chips are attached on a multilayer wiring board and, more particularly, to a cooling structure including a plurality of expandable microbellows.
Hitherto, with an increase in degree of integration of semiconductor electronic circuit, an amount of heat which is generated from one semiconductor chip has increased more and more and in order to cope with this increase in the heat generation, new means for cooling the chips having an excellent cooling efficiency has been studied. Particularly, for the high speed data processing apparatus such as a computer in which the heat generation amount of the chip exceeds ten watts and it is necessary to severely manage the operating temperature range of the chip, the cooling apparatus using the liquid as disclosed in, e.g., U.S. Pat. No. 4,138,692 has been proposed. In such a kind of apparatus, to reduce the thermal resistance from the semiconductor chip to the cooling medium, it is necessary to couple them by a high thermal conductivity material. At the same time, since the heights and angles of inclination of the respective chips differ due to the deformation of the substrate or unevenness of soldering, it is necessary to provide the expandable movable part in the connecting portion to thermally couple the piping system to supply the cooling medium with the semiconductor chip. As a structure of the movable part, it is considered that the bellows is the most flexible optimum structure as frequently seen in vacuum vessels or the like. As shown in FIG. 1, as a method of manufacturing the bellows, it is considered to arc-weld or braze respective bellows component parts 106 injunctions 105 by use of arcs 103 and 104. However, in the actual high speed data processing apparatus, nearly one hundred semiconductor chips are attached to a square substrate in which a length of each side is 100 mm. Therefore, even if one cooling block is connected for one chip and at least one bellows is attached thereto, the size of outer diameter becomes below 10 mm, so that according to the conventional technology, the microbellows can be formed by only an electroplating method as shown in FIG. 2. In FIG. 2, reference numeral 107 denotes a power source; 108 is a plating bath; 109 a plating fluid; 110 an original mold; 111 a plated film; and 112 a plating electrode. The shape of the electroforming bellows manufactured by the electroplating method has a limitation, so that the number of mountains per unit length cannot be increased and the plated film quality becomes hard. Consequently, only the bellows having a high spring constant can be produced. On the other hand, in the junction between the piping system and the bellows or between the bellows and the cooling block, a pressure cannot be applied to the junction surfaces in terms of the structure of the electroforming bellows, so that the junction can be made by only the brazing means due to the replaced brazing. However, according to the brazing, a flux must be used to improve thermal flowout of a brazing material and wettability and thereby to improve junction property. Thus, if the residue remains, there will be a significant adverse influence on the corrosion. In addition, defects are likely to occur in the brazing, portion and the reliability for airtightness also will be lacking. Further, the structural material and brazing material cannot have the same composition, so that in the case where the water is used as the cooling fluid, electrochemical corrosion occurs near the boundary between the structural material and the brazing material layer and there is the problem such that the corrosion resistance significantly deteriorates. On the other hand, a Kovar material is generally used as a material of the housing or cooling block in consideration of the thermal expansion difference between this material and SiC ceramics which are used as a multilayer wiring board or electrical insulation layer of the cooling block. However, as a bellows material as well, it is desirable to use the Kovar material of the same quality in terms of the electrochemical corrosion. However, it is difficult to produce the bellows made of alloy according to the conventional electroplating method and there is the problem such that the bellows material is limited to the pure metal such as Ni. Further, in the case of assembling the cooling structure using the electroforming bellows, about a hundred of bellows must be brazed to the housing in which a length of each side is about 100 mm and the piping system is built therein, so that it takes a long time to set the bellows, brazing material, consequently flux and the productivity deteriorates.